CWRU researchers among team discovering “remarkably complete” cranium of early human ancestor species
Yohannes Haile-Selassie—a Case Western Reserve University adjunct professor and curator at the Cleveland Museum of Natural History—and a team of researchers have discovered a “remarkably complete” cranium of a 3.8-million-year-old early human ancestor in Ethiopia.
Working for the past 15 years at the Woranso-Mille paleontological site—located in the country’s Afar region—the team unearthed the cranium in February 2016; in the years since, they have conducted extensive analyses of the fossil, while geologists determined the age and context of the specimen—and made significant discoveries that increase our understanding of early human ancestors.
The results of the team’s findings are published online in two papers in the international scientific journal Nature.
The cranium represents a time interval—between 4.1 and 3.6 million years ago—from which early human ancestor fossils are extremely rare.
The findings also indicate that Lucy’s species (Australopithecus afarensis) and the early human ancestor species of the cranium (Australopithecus anamensis) coexisted for approximately 100,000 years, challenging previous assumptions of a linear transition between these two early human ancestors.
“This is a game-changer in our understanding of human evolution during the Pliocene,” said Haile-Selassie, an adjunct professor of anthropology and cognitive science in Case Western Reserve’s College of Arts of Sciences.
Due to the cranium’s rare near-complete state, the researchers also identified never-before-seen facial features in the species.
“[The early human ancestor] has a mix of primitive and derived facial and cranial features that I didn’t expect to see on a single individual,” Haile-Selassie said.
The A. anamensisspecies was previously only known through teeth and jaw fragments, all dated to between 4.2 and 3.9 million years ago, and researchers determined similarities between the preserved dentition of the cranium and these previously found fragments.
Beverly Saylor—a professor in the Department of Earth, Environmental, and Planetary Sciences at Case Western Reserve—and her colleagues determined the age of the fossil using an array of techniques.
By looking at the magnetic properties and chemistry of volcanic rock layers nearby the fossil—and combining field observations with an analysis of microscopic biological remains—Saylor and her colleagues were able to determine the landscape, vegetation and hydrology where (and when) the early human ancestor died.
The findings were published in a companion paper published in the same issue of Nature.
Reconstructing a pre-historic landscape
The early human ancestor likely lived near a large lake in a region that was dry, according to the findings.
The cranium was found in sandy deposits of a delta where a river entered a lake.
The river likely originated in the highlands of the Ethiopian plateau, while the lake developed at lower elevations—where rift activity caused the Earth’s surface to stretch and thin, creating the lowlands of the Afar region.
Volcanic debris flows occasionally descended into the otherwise quiet lake, which was ultimately buried by basalt lava flow—a dramatic landscape change common in rift settings.
“Incredible exposures and the volcanic layers that episodically blanketed the land surface and lake floor allowed us to map out this varied landscape and how it changed over time,” said Saylor.
Also, fossil pollen grains and chemical remains of fossil plant and algae were preserved in the lake and delta sediments and provided clues about the ancient environmental conditions—specifically indicating that the lake near where the early human ancestor finally rested was likely salty at times and its watershed was mostly dry.
Yet, there were also forested areas on the shores of the delta or alongside the river that fed the delta and lake system, researchers determined.
A plentiful paleontological project
The Woranso-Mille project has been conducting field research in the central Afar region of Ethiopia since 2004. The project has collected more than 12,600 fossil specimens representing more than 80 mammalian species. The fossil collection includes about 230 fossil hominin specimens older than 3.8 million years to around 3 million years.
The first piece of the cranium fossil—the upper jaw—was found by Ali Bereino, a local Afar worker, on Feb. 10, 2016, at a site around 34 miles north of Hadar (“Lucy’s” site). The specimen was exposed on the surface, and further investigation of the area resulted in the recovery of the rest of the fossil.
“I couldn’t believe my eyes when I spotted the rest of the cranium. It was a eureka moment and a dream come true,” said Haile-Selassie.
An international team
Work on the analysis and geological and paleoenvironmental context of MRD was conducted by an international team of paleoanthropologists, geologists, geochemists and paleobotanists from renowned institutions, including the Max Planck Institute for Evolutionary Anthropology in Germany, Pennsylvania State University and the University of Bologna in Italy.
Work to understand the age and landscape setting included researchers from the Universitat de Barcelona in Spain, the Berkeley Geochronology Center in California, Addis Ababa University in Ethiopia, Franklin and Marshall College in Pennsylvania. Reconstructing the environmental conditions was conducted by researchers at University of Michigan, University of Southern California, Los Angeles, and Aix-Marseille University in France.
A co-author on both Nature papers, Stephanie Melillo, of the Max Planck Institute for Evolutionary Anthropology in Germany, graduated from Case Western Reserve in 2005 with a Bachelor of Arts in anthropology.
For more information, contact Bill Lubinger at email@example.com.